Method for setting, calibrating, and verifying an occupation classification system threshold

ABSTRACT

The invention is directed to a method for setting an occupant classification system threshold for a vehicle occupant detection system, the method comprising collecting occupant classification system data for a seat, the data being indicative of occupant weight, analyzing the data to determine where a separation exists between an occupant for which a restraint should be suppressed and an occupant for which the restraint should be deployed, and analyzing the data to determine a worst case child suppression weight and shape, which is based at least on where the separation exists. The worst case child suppression weight and shape define the occupant classification system threshold.

This is a division of application Ser. No. 11/475,107, filed Jun. 27,2006, now U.S. Pat. No. 7,477,975, which is incorporated herein byreference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of Invention

This invention relates to the field of setting, calibrating, andverifying an occupant classification system (OCS) threshold. Morespecifically, this invention relates to a simplified and accurate methodof setting an OCS threshold for a type of vehicle seat and thencalibrating and verifying seats of the same type following manufacture.

2. Background

To limit the risk of death or serious injury in the event of a crash,many vehicles include passenger airbags, which are designed to deployunder certain crash conditions. Various types of sensors and crashcriteria are commonly used to detect crash conditions for whichpassenger airbag deployment is desirable.

It is known that, even given a crash condition for which passengerairbag deployment is desirable, deployment of an airbag can itself causeinjuries when the occupant of the passenger seat is a small child orinfant. Accordingly, federal regulations have been developed requiring asystem for determining whether a passenger seat is occupied by a smallchild or an infant, in which case airbag deployment should besuppressed.

In addition, if the passenger seat is unoccupied, deployment of thepassenger airbag is unnecessary. Unnecessary deployment of the passengerairbag can increase the cost of repairing the vehicle.

Vehicle occupant detection systems judge whether, and how forcefully, todeploy a restraint such as a passenger airbag. One fundamental parameterin judging deployment is the weight of the seat occupant, as weight maybe used to distinguish between an adult and an infant or small child.For example, Federal Motor Vehicle Safety Standard (FMVSS) 208 requiresthat an airbag be suppressed for a child less than six years old, but bedeployed for an adult in the 5^(th) percentile. A 5^(th) percentileadult weighs, for example, 103-113 pounds standing, with a seated weightof about 77-85 pounds. A 6-year-old child weighs, for example, 52.5pounds when seated. Thus, a separation exists between the seated weightof a small adult and a six year old child.

A known way of estimating occupant weight is by measuring pressure in afluid-filled bladder disposed in or under a foam seat cushion. Increasedweight on the seat increases pressure in the bladder. A pressure sensorconnected to the bladder generates output signals indicative of pressurein the bladder and therefore occupant weight. Because a separationexists between the seated weight of a small adult and a 6-year-old, aseparation similarly exists for pressure in the bladder and thereforethe output signals of the pressure sensor.

In a crash situation, a microprocessor determines whether the outputsignals from the passenger seat pressure sensor exceeds a thresholdvalue indicative of adult occupancy. If so, deployment of the passengerairbag is enabled. If not, it is assumed that the passenger seat isempty or the occupant of the seat is a small child or an infant, anddeployment of the airbag is suppressed or limited accordingly.

Vehicle manufacturers must calibrate and verify calibration of theseoccupant detection systems. A conventional calibration and verificationsystem applies a weight to the vehicle seat. Data corresponding to theapplied weight is output from the seat's pressure sensor. The data isprocessed by a controller of the occupant detection system andcalibration values are calculated, which include the threshold valueindicative of adult occupancy. The calibration values are typicallystored in an EEPROM. The weight is applied to the seat again, and theverification values are calculated again. If the calibration andverification values for the weight applications are within a specifiedtolerance, the occupant detection system is acceptable for use. Thiscalibration and verification system can also be used to program thecontroller of the occupant detection system.

BRIEF SUMMARY OF THE INVENTION

In one embodiment, the invention is directed to a method for setting anoccupant classification system threshold for a vehicle occupantdetection system, the method comprising collecting occupantclassification system data for a seat, the data being indicative ofoccupant weight, analyzing the data to determine where a separationexists between an occupant for which a restraint should be suppressedand an occupant for which the restraint should be deployed, andanalyzing the data to determine a worst case child suppression weightand shape, which is based at least on where the separation exists. Theworst case child suppression weight and shape define the occupantclassification system threshold.

In another embodiment, the invention is directed to a method forcalibrating an occupant classification system threshold for a vehicleoccupant detection system, the method comprising collecting occupantclassification system data for a seat, the data being indicative ofoccupant weight, analyzing the data to determine where a separationexists between an occupant for which a restraint should be suppressedand an occupant for which the restraint should be deployed, analyzingthe data to determine a worst case child suppression weight and shape,which is based at least on where the separation exists, providing aweight drop head having the worst case child suppression shape, applyingthe worst case child suppression weight to a seat of the type for whichthe occupant classification system data was collected using the weightdrop head having the worst case child suppression shape, recording asignal indicative of the applied worst case child suppression weight andshape, and recording the occupant classification system threshold basedon the signal.

In yet another embodiment, the invention is directed to a method forverifying an occupant classification system threshold for a vehicleoccupant detection system, the method comprising collecting occupantclassification system data for a seat, the data being indicative ofoccupant weight, analyzing the data to determine where a separationexists between an occupant for which a restraint should be suppressedand an occupant for which the restraint should be deployed, analyzingthe data to determine a worst case child suppression weight and shape,which is based at least on where the separation exists, providing aweight drop head having the worst case child suppression shape, applyingthe worst case child suppression weight to a seat of the type for whichthe occupant classification system data was collected using the weightdrop head having the worst case child suppression shape, recording afirst signal indicative of the applied worst case child suppressionweight and shape, applying the worst case child suppression weight tothe seat using the weight drop head having the worst case childsuppression shape, recording a second signal indicative of the appliedworst case child suppression weight and shape, and verifying that thefirst and second signals are within a specified tolerance.

In yet another embodiment, the invention is directed to a device forcalibrating an occupant classification system threshold for a vehicleoccupant detection system, the device comprises a force applicationmechanism, a weight drop head having a worst case child suppressionshape and being attached to the force application mechanism, andcontrols that move the weight drop head and activate the forceapplication mechanism to apply a force to a vehicle seat that isrepresentative of a worst case child suppression weight for that seat. Apressure measurement device in the vehicle seat outputs a signalindicative of the applied force, the occupant classification systemthreshold being calibrated based on the signal.

Further features of the present invention, as well as the structure ofvarious embodiments of the present invention are described in detailbelow with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and form partof the specification, illustrate the present invention and together withthe description, further serve to explain the principles of theinvention and to enable a person skilled in the pertinent art to makeand use the invention. In the drawings, like reference numbers indicateidentical or functionally similar elements.

FIG. 1 illustrates a prior art vehicle seat including a fluid-filledbladder and an associated pressure sensor.

FIG. 2 graphically depicts pressure increasing monotonically withoccupant weight applied to the fluid-filled bladder of FIG. 1.

FIG. 3 schematically illustrates a prior art controller for receivingoutput from the pressure sensor of FIG. 1.

FIG. 4 is a flow chart showing an exemplary method of setting,calibrating, and verifying occupant classification system thresholds inaccordance with the present invention.

FIG. 5 illustrates a vehicle seat and an exemplary weight drop headdesigned in accordance with the present invention.

FIG. 6 illustrates an exemplary machine for utilizing the weight drophead of FIG. 5 to calibrate and verify occupant classification systemthresholds in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention includes a device and a method for setting,calibrating, and verifying occupant classification system thresholds fora variety of conventional vehicle seats. A vehicle seat 10 typicallyincludes a bottom cushion 12 and a back cushion 14. The cushions 12, 14typically comprise foam. A bladder 16 is disposed in or under the bottomcushion 12 and commonly extends parallel with the central seatingsurface. The bladder 16 may contain a fluid such as silicone.

The bladder 16 is preferably coupled to a pressure sensor 20 thatprovides an electrical output signal indicative of the fluid pressure inthe bladder 16, for example in the form of A/D counts. This pressuresignal is provided as an input to a controller 22 that preferably candetermine whether the seat 10 is unoccupied, occupied by a small childor an infant, or occupied by an adult. The determination of seatoccupancy is preferably based on the bladder pressure and canadditionally be based on other inputs, such as atmospheric pressure,temperature, and humidity. The pressure signal may additionally be usedas a factor in determining how forcefully to deploy airbags or otherpyrotechnically-deployed restraints during a crash event.

Other suitable pressure measurement devices may alternatively beemployed, and may include a separate pressure sensor as needed.

In general, the fluid in the bladder 16 has a given nominal or unloadedpressure, which increases monotonically with occupant weight applied tothe bottom cushion 12, as graphically depicted in FIG. 2. The line 24represents the pressure (A/D counts) vs. weight (pounds) relationship ofa given vehicle seat, which line varies for differing vehicle seatsbased on, for example, the shape and construction of the seat, and thelocation of the bladder within the seat.

FIG. 3 shows an exemplary embodiment of an occupant weight detectionsystem including a controller 22 that provides an output signalindicating whether airbag deployment should be inhibited or allowedbased on at least a pressure reading indicative of occupant weight. Avehicle ignition voltage V_(ign) is supplied to the controller 22, and avoltage regulator 30 provides a regulated system voltage. Regulatedsystem and ground voltages are supplied to the pressure sensor 20 and amicroprocessor 32. The microprocessor 32 has analog-to-digital (A/D)input channels that receive the ignition voltage V_(ign), the systemvoltage from the voltage regulator 30, and the pressure sensor outputvoltage.

Loads applied to a vehicle seat can have different footprints. Forexample, the human body (or an anthropomorphic test dummy (ATD)) has adifferent footprint than a safety seat (which may include, for example,a rearwardly-facing infant seat (RFIS), a forward-facing child seat(convertible or non-convertible), and a booster seat). RFIS in generalhave varying footprints. Further, booster seats and forward-facing childseats can be used in passenger seats and have a variety of footprints.Different load footprints can cause different pressure signals for thesame weight. For each type of seat, a “worst case” footprint can bedetermined. The worst case footprint is the footprint that produces thehighest pressure reading for a given weight or class of occupant (e.g.,a 12-month-old in a RFIS, a 3-month-old in forward-facing child seat, ora 6-year-old with or without a booster seat). The present inventioncontemplates determining a worst case footprint for each type of vehicleseat, and using that worst case footprint to set, calibrate, and verifythe occupant detection system threshold for that type of seat.

FIG. 4 illustrates a method for setting and calibrating occupantdetection systems for four types of vehicle seats, referred to as TypeA, Type B, Type C, and Type D. Initially, FMVSS 208 raw OCS data iscollected for at least one seat of each type. FMVSS 208 raw OCS data iscollected for a seat by positioning different RFIS, forward-facingseats, boosters, and ATDs in the seat in one or more positions withappropriate weights as required by regulation. Appropriate weightspresently include the weight off a 12-month-old for a RFIS, the weightof a 3-year-old (e.g., 34.5 lbs) for a forward-facing child seat, theweight of a 6-year-old (e.g., 52.5 lbs) for both a booster seat and anATD, and the weight of a 5^(th) percentile adult (e.g., 108 lbs) for anATD.

As an example, FMVSS 208 may require eight test cases for a 6-year-old,including four positions of an ATD (including leaning all the way backin a seat, reclining the seat back, and leaning against the vehicledoor) and four different types of safety seats. Each of the requiredtest cases is preferably performed for each seat according to regulationand the resulting data is collected for each seat in the form of A/Dcounts.

Next, for each seat type, the data is analyzed to determine where theseparation exists between six year old data and 5^(th) percentile adultdata. After the separation is identified, a “worst case childsuppression” from FMVSS 208 is defined. The worst case child suppressionis the weight and corresponding load footprint for which the highestpressure readings occur for a child or infant in an appropriate seat.The worst case child suppression cases are defined as Suppress_A,Suppress_B, Suppress_C, and Suppress_D. Suppress_A through Suppress_Dcorrespond to the FMVSS test scenario that created the highest A/D countoutput from the pressure sensor 20. Typically, Suppress_A thoughSuppress_D is a 6-year-old, either in a booster or not.

After Suppress_A through Suppress_D are defined, they are compared todetermine whether any or all of them are the same. If all of them arethe same, the present invention contemplates building a single weightdrop head, as described below, having a footprint representative of thatworst case child suppression. If Suppress_A through Suppress_D are notsame, a weight drop head is preferably built for each of the commonworst case child suppressions. For example, if none of Suppress_Athrough Suppress_D are the same, four weight drop heads are preferablybuilt.

The present invention also contemplates that there may be a degree ofcommonality that would allow a single weight drop head to be built formore than one of Suppress_A through Suppress_D based on a given degreeof similarity, even though they are not exactly the same.

In a preferred embodiment of the invention, after a seat ismanufactured, the weight drop head built for that seat type based on theworst case child suppression is applied to the surface of the bottomcushion 12 of the seat on the same area as the actual test case asdefined above. A force is applied to the weight drop head that isrepresentative of the appropriate worst case child suppression weight(e.g., 52.5 lbs for the representative 6-year-old, plus added weight forthe booster seat if the worst case includes a booster seat). Thepressure signal from the pressure sensor 20 is recorded in the seat'scontroller 22 for seat calibration during loading. Loading and pressuresignal recordation preferably occurs a number of times for each seat, tocreate data points for that seat. In a particularly preferred embodimentof the invention, a robustness factor is added to the data points andrecorded in the seat's controller as the passenger airbag ON/OFFthreshold or the occupant classification system threshold. However, thepresent invention also contemplates the passenger airbag ON/OFFthreshold being recorded based on the data points without using arobustness factor. The controller uses the passenger airbag ON/OFFthreshold in determining an appropriate signal to send to the vehicle'ssafety system ECU.

Verification of the occupant classification system threshold can occurduring or after calibration, and is achieved by the values of the datapoints being within a specified tolerance.

FIG. 5 represents a vehicle seat 10 and the factors that effect thepressure distribution of a given load on its bottom cushion 12 andtherefore on the bladder 16 located in or under the bottom cushion 12.As can be seen, some of the factors effecting pressure distribution of aload on the bladder 16 include:

-   -   The position of the load on the bottom cushion 12 in both the X        and Y directions (side-to-side and front-to-back, respectively).    -   The angle of the seat back cushion 14.    -   The angle of the seat bottom cushion 12.

Thus, when the weight drop head 50 built for a given seat type based onthe worst case child suppression is to be applied to the surface of thebottom cushion 12 on the same area as the actual test case, the positionof the weight drop head should preferably be the same with respect to atleast the above three criteria.

FIG. 6 discloses an exemplary embodiment of a weight drop head 50 and acalibrating machine 60 for utilizing the weight drop head 50 to apply aforce to a seat 10. To calibrate and verify a manufactured vehicle seat10 in accordance with the present invention, a weight drop headcorresponding to the correct worst case child suppression is attached tothe calibrating machine 60. The calibrating machine 60 includes controls62 (not shown in detail) that move the weight drop head 50 to anappropriate position above the seat's bottom cushion 12 and lower theweight drop head 50 to apply a force equal to the worst case childsuppression weight, via a force application mechanism, to the seat'sbottom cushion 12 a predetermined number of times. During eachapplication of a force, the pressure signal from the pressure sensor 20is recorded in the seats controller 22 and used as specified above.

While known methods of seat calibration and verification use a weightreading, which requires normalization (i.e., conversion from pressuredata to weight data), the present invention allows the seat to becalibrated and verified using only the pressure data, preferably in A/Dcounts.

1. A device for calibrating an occupant classification system thresholdfor a vehicle occupant detection system, the device comprising: a forceapplication mechanism; a weight drop head having a worst case childsuppression shape and being attached to the force application mechanism;and controls that move the weight drop head and activate the forceapplication mechanism to apply a force to a vehicle seat that isrepresentative of a worst case child suppression weight for that seat,wherein a pressure measurement device in the vehicle seat outputs asignal indicative of the applied force, the occupant classificationsystem threshold being calibrated based on the signal.
 2. The device ofclaim 1, wherein the worst case child suppression shape corresponds tothe shape of a footprint of a rear-facing infant seat.
 3. The device ofclaim 1, wherein the worst case child suppression shape corresponds tothe shape of a forward-facing child seat.
 4. The device of claim 1,wherein the worst case child suppression shape corresponds to the shapeof a booster seat.
 5. The device of claim 1, wherein the worst casechild suppression shape corresponds to the shape of a child's rear end.6. A device for setting, calibrating, and verifying an occupantclassification system threshold for a vehicle occupant detection system,the device comprising: a force applicator; a weight drop head having aworst case child suppression shape and being attached to the forceapplication mechanism; a pressure measurement device configured tomeasure a force applied by the force applicator and weight drop head;and controls configured to activate the force applicator to apply aforce to the pressure measurement device that is representative of aworst case child suppression weight, wherein, when a force is applied tothe pressure measurement device by the force applicator and weight drophead, the pressure measurement device outputs a signal indicative of theapplied force for use in setting, calibrating, and verifying theoccupant classification system threshold.
 7. The device of claim 6,wherein the worst case child suppression shape corresponds to the shapeof a footprint of a rear-facing infant seat.
 8. The device of claim 6,wherein the worst case child suppression shape corresponds to the shapeof a forward-facing child seat.
 9. The device of claim 6, wherein theworst case child suppression shape corresponds to the shape of a boosterseat.
 10. The device of claim 6, wherein the worst case childsuppression shape corresponds to the shape of a child's rear end.